Spacecraft in low earth orbit or other low orbits (LEO spacecraft) carry antennas to downlink observational data at a high rate. The data can be downlinked in real time as the observations are made when the LEO spacecraft is in view of a ground station. During periods of time when the LEO spacecraft is not in view of a ground station, the data may be stored aboard the spacecraft to be sent to a ground station at a later time when the LEO spacecraft comes into view of the ground station. For a practical number and geographic distribution of ground stations, in the absence of the presently disclosed techniques, low-latency access to the observational data is impossible for significant portions of the LEO spacecraft's time in orbit.